An example of a technique for maintaining a previously calibrated mobile device positioning system to account for changes in perturbers of the Earth's magnetic field. A mobile device obtains a corrected heading estimate of the mobile device within a space based on a previously recorded heading correction value. The mobile device also calculates a device heading relative to a previously orientated map of the space. The mobile device subsequently updates the heading correction value with any deviation between the corrected heading estimate and the calculated device heading.